PbCa2[Al8O15] with a novel three‐dimensional aluminate anion

The asymmetric unit of the title compound, lead(II) dicalcium octaaluminate, contains one Pb, one Ca, four Al and eight O atoms, with the Pb atom and one O atom situated on mirror planes. Three Al atoms exhibit slightly distorted tetrahedral coordinations with a mean Al—O bond length of 1.76 Å. The fourth Al atom is in a considerably distorted trigonal–bipyramidal coordination with a mean Al—O bond length of 1.89 Å. One AlO₄ tetrahedron forms infinite chains parallel to 100] via corner‐sharing. These chains are linked by parallel chains of edge‐sharing AlO₅ trigonal bipyramids into layers A of six‐membered double rings extending parallel to (010). The second layer B is made up of the remaining two AlO₄ tetrahedra. These tetrahedra share corners, resulting in likewise six‐membered double rings. Finally, the parallel layers A and B are linked into a three‐dimensional framework by common corners. Charge compensation is achieved by the Pb²⁺ and Ca²⁺ cations, which are situated in the cavities of the anionic framework, and which are surrounded by seven and six O atoms, respectively, both within highly irregular coordination polyhedra.